I have a flywheel that I pulled off a 454. I had assumed that it was a 350 flywheel, since they swapped in the 454 replacing a 350, and they had used a balance plate that was bolted between the flywheel and crank.

I just had that flywheel re-surfaced to use on a 350, and I noticed 4 balancing holes drilled on the front of it. (left flywheel, bottom left of pic)

Did some 350 flywheels have balance holes drilled in them like this? (the flywheel on the right of the picture is a 350 flywheel for sure).

Those holes are drilled for balance.... they are only to neutral balance the flywheel. This is required due to some casting irregularities. A non-counterweighted flywheel would likely require more drilling than possible to make it compatible with a 454. In these applications (400, 454 &amp; late model 1pc. seal engines)you require weight to be added not subracted.

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